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iluwatariluwatar
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added interpreter sample
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‎interpreter/pom.xml‎

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<?xml version="1.0"?>
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<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
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<modelVersion>4.0.0</modelVersion>
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<parent>
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<groupId>com.iluwatar</groupId>
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<artifactId>java-design-patterns</artifactId>
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<version>1.0-SNAPSHOT</version>
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</parent>
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<groupId>com.iluwatar</groupId>
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<artifactId>interpreter</artifactId>
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<version>1.0-SNAPSHOT</version>
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<name>interpreter</name>
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<url>http://maven.apache.org</url>
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<dependencies>
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<dependency>
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<groupId>junit</groupId>
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<artifactId>junit</artifactId>
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<version>3.8.1</version>
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<scope>test</scope>
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</dependency>
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</dependencies>
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</project>

‎interpreter/src/main/java/com/iluwatar/App.java‎

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package com.iluwatar;
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import java.util.Stack;
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public class App
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{
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/**
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*
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* Expressions can be evaluated using prefix, infix or postfix notations
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* This sample uses postfix, where operator comes after the operands
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*
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*/
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public static void main( String[] args )
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{
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String tokenString = "4 3 2 - 1 + *";
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Stack<Expression> stack = new Stack<>();
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String[] tokenList = tokenString.split(" ");
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for (String s : tokenList) {
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if (isOperator(s)) {
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Expression rightExpression = stack.pop();
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Expression leftExpression = stack.pop();
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System.out.println(String.format("popped from stack left: %d right: %d",
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leftExpression.interpret(), rightExpression.interpret()));
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Expression operator = getOperatorInstance(s, leftExpression,
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rightExpression);
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System.out.println(String.format("operator: %s", operator));
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int result = operator.interpret();
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NumberExpression resultExpression = new NumberExpression(result);
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stack.push(resultExpression);
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System.out.println(String.format("push result to stack: %d", resultExpression.interpret()));
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} else {
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Expression i = new NumberExpression(s);
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stack.push(i);
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System.out.println(String.format("push to stack: %d", i.interpret()));
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}
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}
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System.out.println(String.format("result: %d", stack.pop().interpret()));
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}
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public static boolean isOperator(String s) {
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if (s.equals("+") || s.equals("-") || s.equals("*"))
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return true;
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else
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return false;
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}
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public static Expression getOperatorInstance(String s, Expression left,
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Expression right) {
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switch (s) {
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case "+":
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return new PlusExpression(left, right);
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case "-":
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return new MinusExpression(left, right);
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case "*":
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return new MultiplyExpression(left, right);
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}
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return null;
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}
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}

‎interpreter/src/main/java/com/iluwatar/Expression.java‎

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package com.iluwatar;
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public abstract class Expression {
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public abstract int interpret();
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@Override
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public abstract String toString();
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}

‎interpreter/src/main/java/com/iluwatar/MinusExpression.java‎

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package com.iluwatar;
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public class MinusExpression extends Expression {
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private Expression leftExpression;
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private Expression rightExpression;
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public MinusExpression(Expression leftExpression, Expression rightExpression) {
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this.leftExpression = leftExpression;
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this.rightExpression = rightExpression;
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}
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@Override
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public int interpret() {
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return leftExpression.interpret() - rightExpression.interpret();
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}
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@Override
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public String toString() {
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return "-";
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}
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}

‎interpreter/src/main/java/com/iluwatar/MultiplyExpression.java‎

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package com.iluwatar;
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public class MultiplyExpression extends Expression {
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private Expression leftExpression;
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private Expression rightExpression;
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public MultiplyExpression(Expression leftExpression, Expression rightExpression) {
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this.leftExpression = leftExpression;
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this.rightExpression = rightExpression;
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}
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@Override
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public int interpret() {
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return leftExpression.interpret() * rightExpression.interpret();
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}
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@Override
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public String toString() {
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return "*";
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}
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}

‎interpreter/src/main/java/com/iluwatar/NumberExpression.java‎

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package com.iluwatar;
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public class NumberExpression extends Expression {
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private int number;
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public NumberExpression(int number) {
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this.number = number;
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}
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public NumberExpression(String s) {
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this.number = Integer.parseInt(s);
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}
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@Override
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public int interpret() {
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return number;
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}
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@Override
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public String toString() {
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return "number";
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}
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}

‎interpreter/src/main/java/com/iluwatar/PlusExpression.java‎

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package com.iluwatar;
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public class PlusExpression extends Expression {
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private Expression leftExpression;
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private Expression rightExpression;
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public PlusExpression(Expression leftExpression, Expression rightExpression) {
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this.leftExpression = leftExpression;
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this.rightExpression = rightExpression;
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}
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@Override
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public int interpret() {
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return leftExpression.interpret() + rightExpression.interpret();
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}
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@Override
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public String toString() {
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return "+";
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}
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}

‎pom.xml‎

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<module>proxy</module>
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<module>chain</module>
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<module>command</module>
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<module>interpreter</module>
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</modules>
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<build>

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